We have computed a set of models of white dwarfs. The equation of state is the Chandrasekhar (1939) one corrected by Salpeter (1961). It takes into account both the interactions between particles and the effect of non-zero temperature.
The models consist of an isothermal core with 50% of carbon and 50% of oxygen, surrounded by an envelope of population I composition with 70% of hydrogen and 3% of metals by mass. Nuclear energy is liberated by p-p reactions located in a shell at the edge of the isothermal core. Equilibrium models of various masses and luminosities have been built; Table I gives the values of their characteristic parameters. The central temperature-luminosity-mass relation for our models is compared with the Schatzman (1952) one for pure hydrogen envelopes (S), the Hubbard and Wagner (1970) one for Mg core and solar composition envelope models (HW) and the Van Horn (1970) one for carbons models (VH) (Figure 1). At high luminosities there is a sensible departure from the linear relation. Though our models are not evolutionary sequence ones, they fit very well with the sequences calculated by Vila (1966, 1967). The models studied here are of the type expected from the calculation of the evolution of some double systems (Lauterborn, 1970) after the white dwarfs have lost their very diluted envelopes.